(4R,5S,6S)-3-[[(3S,5S)-5-(dimethylcarbamoyl)-3-pyrrolidinyl]thio]-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid of Formula I, commonly known as meropenem, is a synthetic, broad-spectrum, carbapenem antibiotic.

Meropenem is commercially available as a trihydrate. Several processes for the preparation of meropenem and meropenem trihydrate are described in U.S. Pat. No. 4,888,344; WO Nos. 2006/035300; 2007/029084; 2007/104221; and 2005/118586.
Meropenem trihydrate is generally prepared by dissolving crude meropenem in water followed by cooling and adding a water miscible organic solvent such as acetone or isopropanol. This method requires heating of meropenem and water mixture to achieve complete dissolution and subsequent cooling of the solution along with the addition of water-miscible solvents, and optionally seed crystals, to maximize the precipitation or crystallization of meropenem trihydrate. The present inventors have observed that preparation of meropenem trihydrate from crude meropenem on a large scale results in a increased impurity content, specifically relating to meropenemic acid of Formula II and meropenem dimer of Formula III. The presence of impurities also impacts the yield.

The present inventors have not found that the problems associated with increased impurities, and the corresponding reduced yields, is due to the higher residence time in the batch mode reactors that are commonly employed during the scale-up. In batch mode reactors, the reaction is allowed to proceed for a specified time period after which the mixtures of unreacted materials and/or by-products, along with the desired end product, are withdrawn. After the reactants or starting materials are fed into the batch mode reactor, no further reactants or starting materials are added. The batch mode reactors have more residence time, especially during the heating and subsequent cooling steps. In the case of meropenem, the present inventors have observed that high residence time of meropenem, along with water, leads to decomposition of meropenem and increases impurity formation. On the other hand, the replacement of water with alternate organic solvents, for example, methanol, in which meropenem is freely soluble and does not require a heating step, results in higher residual solvent content.